1. Field of the Invention
The present invention relates to a preparation method of octafluoro-(2,2)-paracyclophane (parylene AF4) and, more particularly, the present invention relates to a catalytic or a photocatalytic preparation method of parylene AF4.
2. Description of Related Art
By using the vacuum pyrolysis chemical vapor deposition (CVD) method, parylene can be made into an extremely thin film which has an excellent uniformity, chemical stability and high transparency. Parylene is widely used in the forms of coating thin film, for application on the electrical isolation of printed circuit board, moisture protection of sensors or medical equipment, insulating layers of electrical unit, various protective films or packing materials, and preventing corrosion of metal coatings.
Recently, due to high melting point (about 450° C.) and low dielectric constant (about 2.2) of the fluorinated parylene polymers, such as poly(tetrafluoro-para-xylene) (parylene HT), with its structure shown in formula (1), compared to the traditional parylene N, parylene C, and parylene D, it has superior anti-UV properties, aging resistance, and thermal stability.

In addition, parylene HT can be coated on various irregular substrates' surface, for example, glass, metal, resin, plastic, ceramic and paper. The products coated with parylene HT usually have excellent anti-corrosion, anti-moisture, and insulation protection performance, with the advantages of ultra-thin, transparent, and pinholes free, parylene HT can be used in electronic units, automotive industries, solar energy industries, and the low dielectric constant films of semiconductor industries. Currently, the coating of parylene HT is prepared via CVD process. During the CVD process, free radical monomers are produced and then polymerized into parylene HT on the surface of the object: the method is different from the other general preparation via liquid coating methods (such as dip-coating, spray-coating, sputter-coating, and plasma-coating). The coating process first includes the vaporization of fluorinated parylene dimer, such as parylene AF4 (formula (2)); then forming fluorinated para-xylene radicals by high-temperature pyrolysis; finally deposited on the coated substrate; and polymerized to poly(tetrafluoro-para-xylene), which is commonly named parylene HT, as shown in formula (1), on the surface of the coated object.

The mechanism of the parylene AF4 polymerized to parylene HT via CVD is shown in formula (3).

Many synthetic methods of parylene AF4 has been published in the literature, which mainly use 1,4-bis(chlorodifluoromethyl)benzene (CFB), shown in formula (4), to react with reducing agent Zinc (Zn) and obtain the parylene AF4. In the previous methods, however, in order to prevent the undesired byproducts formation, the reactions were usually carried out in highly diluted conditions, that is, large amount of solvents are necessary in the synthetic methods, therefore, the purchase and storage of the solvent, the process of feeding and the removal of the solvent or impurities will increase the cost of the preparation, coupled with long reaction time, more byproducts and complication of parylene AF4 purification procedure, those methods are not suitable for mass productions.

Therefore, there is a need for the development of a parylene AF4 (octafluoro-[2,2]-paracyclophane) preparation method characterized by high reactant concentration, short reaction time, low cost, less byproducts, easy purification, good reproducibility and stable yield.